1. Field of the Invention
This invention relates to circuits for controlling the energization of electrically heated vehicle windows. More specifically, this invention relates to a control and energization circuit for temporarily applying large quantities of heat to vehicle windows to deice the windows. More specifically still, this invention relates to a circuit for temporarily interrupting the charging cycle of a vehicle battery to apply substantially the entire vehicle alternator output to the electrical resistance window heating elements. More specifically still, the present invention relates to such a circuit which includes protective features to assure that the duration of actuation is brief and subject to available electrical energy for battery operation of other vehicle circuits, that unnecessary actuation is avoided, and that too rapid reactuation is avoided.
2. Description of the Prior Art
Electrical heated rear windows are in common use, and it has been proposed to use electrically heated windscreens. The latter would have the advantage of allowing hot air ducts between the heater matrix and the screen to be dispensed with. Such heated vehicle windows as are in use and as are proposed receive electric energy at an essentially fixed and constant rate. A constant heating rate as presently used is adequate to demist a vehicle window but is not adequate, owing to limitations in the vehicle electrical system, to remove any substantial ice accumulations (to deice) the vehicle windows. However, if an electrically heated window is to be capable of deicing as opposed to mere demisting, a large amount of power is required. Such a requirement would place a heavy strain on the vehicle electrical system. Alternatively, if such a strain on the vehicle electrical system is to be avoided, the time required for electrical deicing would be so great as to render the system of little practical value.
An object of this invention is to provide a circuit which will permit an improved method of electrically deicing vehicle windows.